For purposes of this disclosure, the term electromagnetic interference (EMI) is understood to refer to electromagnetic emission and radiation that includes both electromagnetic interference and radio-frequency interference (RFI). Both of these types of interference generate electromagnetic fields that can interfere with the operation of adjacent electrical equipment. It is desirable to protect electronic devices from external EMI, and also to prevent internal EMI from escaping and possibly interfering with other electronic devices in the vicinity. To accomplish this, EMI shields comprised of EMI absorbing material are often used in enclosures containing electronic equipment, components, and/or circuitry (e.g., computers and test equipment).
EMI absorbing material provides highly efficient EMI attenuation. However, when dealing with electronic devices generating high levels of EMI within an enclosure, EMI absorbing material is only partially effective in EMI attenuation. Enclosures of electronic devices typically allow for an amplified effect due to EMI. This is due in part to resonance of the EMI waves within the enclosure. Resonance can amplify the EMI occurring in the form of standing waves in the enclosure thus having a greater affect on the electronic devices in the path of these waves. The formation of electromagnetic standing waves produces spikes in amplitude of this interference in areas within the enclosure.
Mode stirrers typically used in reverberation chambers have the ability to distribute these EMI waves in an enclosure in a homogeneous manner. Mode stirrers distribute these EMI waves to eliminate standing waves through resonance by reflecting these waves throughout the enclosure and establishing a uniform statistical distribution of fields throughout the volume. This lowers the net field strength in an area where seams and apertures are located, thus lowering the radiation outside the enclosure from these seams and apertures.